Solvent-based polymeric surface coating and sealant compositions are utilized in a variety of industries, including automobile manufacture, marine coatings for ships, boats, and bridges, industrial and commercial floor coatings, roof coatings, and the like. The roofing industry, in particular, utilizes a variety of solvent-based polymeric coatings, due to the need for high levels of water resistance. Currently, there is a push, particularly in urban areas, to increase the diffuse reflectivity (albedo) of roofs, since increased albedo helps to reduce the so-called “urban heat island phenomenon” common to modern cities. The dark color of common roofing materials, in combination with dark-colored asphalt streets, results in absorption of enormous amounts of solar energy in concentrated urban settings, which manifests itself as heat. This can significantly increase the temperature in a city compared to the surrounding suburban areas, which generally have innate cooling mechanisms, such as water evaporation from vegetation, that mitigate solar heating.
Many municipalities are now encouraging or even requiring application of high-albedo, generally white colored, roof coatings over asphalt or ethylene propylene diene monomer (EPDM) roofs to reduce urban overheating. The major types of white roof coatings in current use are water-based acrylic coatings and hydrocarbon solvent-based, pigmented synthetic elastomer coatings, usually containing a styrene ethylene/propylene styrene block polymer and an adhesive resin for the necessary level of water resistance and pigment adhesion or binding. Water-based coatings are of limited usefulness in some climates because of their susceptibility to rainfall, freezing and high humidity. They also exhibit poor adhesion to some common roofing materials including TPO (thermoplastic polyolefin), EPDM, and asphalt roofs. One significant drawback of such coatings is that they typically cannot be applied directly on an asphalt or EPDM surface. In the case of asphalt, various colored components leach out of the asphalt and into the white coating layer, thus reducing the heat-reflective nature of the coating. With EPDM roofs, these solvent-based coatings cause undesirable levels of swelling and wrinkling when applied directly to the EPDM rubber surface. To avoid these problems, a primer must be applied to the asphalt or the EPDM roof prior to application of the high-albedo coating.
In addition, the hydrocarbon solvents used in the commercial coating compositions (aliphatic hydrocarbons, aromatic hydrocarbons, or mixtures thereof) desirably has a flash point of about 25-38° C., preferably 37-38° C., to reduce the potential fire hazards associated with hydrocarbon solvents. Unfortunately, the drying time of hydrocarbon solvents is inversely related to the flash point. Fast drying times are desirable for efficiency of the workers and to minimize the adhesion of soil, leaves, or other air-born debris to the surface of the roof coating. There is a desire in the industry for faster drying times for solvent-based roof coatings, which cannot be achieved with hydrocarbons alone, due to the fire hazards of the necessary lower flash point solvents, and the higher environmental impact of such solvents.
Accordingly, there is an ongoing need for environmentally acceptable, pigmented, polymer-containing, solvent-based surface coatings, particularly for roof-coatings, with improved properties such as faster drying times, and the ability to be applied without a primer. The present invention fulfills this need.